Cylinder lock and key combinations of this kind are previously known, e.g. from the U.S. Pat. Nos. 3,722,240, 3,499,302, 4,635,455, 4,723,427 and 4,732,022 (all assigned to Medeco Security Locks, Inc.). They provide well functioning and secure mechanisms. Because of the dual lock feature (tumbler pins as well as a side bar locking mechanism), these locks are difficult to manipulate, in particular by picking and/or so called “bumping”.
However, for certain geometrical configurations, it may be possible to inspect an empty lock (without any key in the keyway) and find out the codes relating to the rotational positions of the “gates” or slots which should register with projections on the side bar. If such inspection is successful, it may be less difficult to bypass or open the lock.
In particular, when the keyway is relatively high, to accommodate a key blade with a large height, such as a key blade extending above the rotational axis of the key plug, some of the tumbler pins may be exposed from the inside of the keyway, so that the “gates” or slots (or other recesses or holes) can be identified or sensed, and their relative locations may be determined.